KP Astro Academy I Navin

How to Calculate the Exact Cusp Boundary Using Placidus in Chennai vs London

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I Navin
KP Astrologer & Educator at KP Astro Academy
How to Calculate the Exact Cusp Boundary Using Placidus in Chennai vs London

How do Placidus cusp boundaries differ between Chennai and London?

Because the Placidus house system relies on the time it takes for degrees of the zodiac to cross the local horizon, high-latitude cities like London experience severe house distortion (interception), whereas equatorial cities like Chennai have relatively equal house sizes.

How to Calculate the Exact Cusp Boundary Using Placidus in Chennai vs London
  • Chennai (13° N): Houses are nearly equal (around 30° each). Intercepted signs are extremely rare.
  • London (51° N): Houses can stretch over 50° or shrink to 15°. Intercepted signs are common, radically altering significators.

How to calculate the exact cusp boundary

  1. Determine the precise latitude and longitude of the birth city (e.g., Chennai: 13.0827° N, 80.2707° E).
  2. Calculate the Local Sidereal Time (LST) of birth.
  3. Find the Ascendant (1st Cusp) and Midheaven (10th Cusp).
  4. Trisect the semi-arcs between the Midheaven and Ascendant to find the 11th and 12th cusps.
Location Latitude Range Placidus Distortion Level Intercepted Signs
Chennai (India) Equatorial (13° N) Minimal Extremely Rare
London (UK) Northern (51° N) High Very Common
Reykjavik (Iceland) Extreme North (64° N) Severe (System breakdown) Guaranteed

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